Re: [PATCH] mm: zswap: return -ENOENT when the swap device is gone

[Baoquan He]

On 09/13/26 at 12:51am, Andrew Morton wrote:
> On Sun, 13 Sep 2026 14:30:31 +0800 Baoquan He <hebaoquan@xxxxxxxxxx> wrote:
> 
> > zswap_writeback_entry() returns -EEXIST when get_swap_device() finds no
> > device.  -EEXIST is the shrinker's "page already in swap cache" signal,
> > which makes zswap_shrinker_scan() stop shrinking entirely.  A NULL
> > get_swap_device() instead means the device is being swapped off, so the
> > entry is simply stale.
> > 
> > Return -ENOENT so the shrinker skips the stale entry and keeps scanning.
> > Independent of xswap; affects all swap devices.
> > 
> > ...
> >
> > --- a/mm/zswap.c
> > +++ b/mm/zswap.c
> > @@ -998,7 +998,7 @@ static int zswap_writeback_entry(struct zswap_entry *entry,
> >  	/* try to allocate swap cache folio */
> 
> Comment was always lame ("say why, not what").  It now seems flat out wrong?

Agree, the comment should be moved down to be cloe to
"mpol = get_task_policy(current);" line.

> 
> >  	si = get_swap_device(swpentry);
> >  	if (!si)
> > -		return -EEXIST;
> > +		return -ENOENT;
> 
> mm-new has changed.  I made this

Thanks. Does it need a v2? or just use ther version you tuned.

By the way, which mm branch is suggested to take as a base for mm
patches posting? I usually take mm-unstable branch, seems it's changed
to mm-new now?

> 
> 
> 	/* try to allocate swap cache folio */
> 	si = get_swap_device(swpentry);
> 	if (IS_ERR_OR_NULL(si))
> 		return -ENOENT;
> 
>